The Sixth Amendment
to the Bill of Rights states that in criminal court cases
defendants shall enjoy the right to trial by an “impartial
jury of the State.” Today, the unanimous vote helps
courts to abide by American ideals. Clearly, if any juror
has a doubt about a defendant’s guilt, the unanimity
rule will protect the subject from wrongful punishment, right?
Maybe not.

This is a possibility
that Kellogg School professor Timothy Feddersen came across
in his research, which suggests that during unanimous elections,
people may have an incentive to vote strategically, in a way
that produces unfavorable outcomes.

At the
annual Kellogg Oh Be Joyful faculty and staff dinner in June,
Feddersen received the inaugural Stanley Reiter Best Paper
Award, established to recognize outstanding research published
by a faculty member in the preceding four calendar years,
for his paper “Convicting the Innocent: The Inferiority
of Unanimous Jury Verdicts” (with Wolfgang Pesendorfer),
printed in the American Political Science Review
(vol. 92, no. 1). To understand the theory, he explains, one
must understand that each person has private information that
is relevant to other jurors’ decisions as well.

“If people
voted naively, without knowing information that others may
know, under unanimity rule guilty people would almost always
be acquitted,” notes Feddersen, the Wendell Hobbs Professor
of Managerial Economics and Decision Sciences.

Unlike majority
rule, in which a vote is pivotal if the other voters equally
split their votes between the two alternatives, a vote in
a unanimous election is pivotal only if other voters have
all voted the same way.

“If my vote
is pivotal it is because everyone else has voted to convict,”
Feddersen explains. “If I believe everyone else is voting
on the basis of private information not available to me, then
I may reason that I should not vote to acquit even when I
believe the defendant to be innocent, thus effectively delegating
the group’s decision from me, with my limited information,
to the group.”

Unanimity rule
therefore creates “perverse incentives” for jurors
that may lead to higher probabilities of both acquitting guilty
defendants and convicting innocent ones, than if a rule such
as simple majority had been used, Feddersen contends.

Additionally, this
reasoning could be mutual among voters, so increasing the
size of the jury could actually increase the probability of
convicting an innocent defendant.

Since 1994, Feddersen
has worked with Pesendorfer, examining strategic voting in
elections. In 1997, they published a paper arguing that a
wide variety of voting rules are successful when voting strategically.
Feddersen says the research on the unanimity rule came to
mind as an afterthought.

“When this
research started, we weren’t interested in different
voting rules; we were more interested in participation in
elections, the way elections aggregate information, and the
incentive for people to participate in elections,” he
explains.

Feddersen’s
work is the first to consider the effect of strategic voting
on the unanimity rule, and preliminary experiments have supported
the theory’s predictions. Nevertheless, he cautions
that the theory is not a recommend- ation for reform.

“This is
an abstract mathematical model and not a claim about how people
actually reason. We don’t have much to say about how
people actually make decisions, only that they will have an
incentive to act in a particular way. There are a number of
factors that get in the way of immediately going from this
paper to saying we ought to get rid of the unanimous jury
verdict,” he says.

For example, he
notes, his paper does not consider the process of jury deliberation.
What if people talk to one another before they decide? Then
the voting rule wouldn’t matter because there is no
private information, he points out. Then too, what if people
have other motivations?

Feddersen is looking
to answer some of these questions in his present research
on the impact that ethically minded voters may have on models
of deliberation. “I’m interested in what kinds
of incentives different voting rules create for people to
talk,” he says.

“It appears
that voting by unanimity rule doesn’t promote discussion
as well as some people have thought.”